How concrete gains strength and how to control these

In this article, we will talk about how much time concrete is gaining strength and what ways to control this parameter are available today.

The topic of the article is not accidental, since most of the construction projects are built from year to year with the use of concrete. The popularity of this material does not decrease, but on the contrary increases, despite the widespread introduction of alternative technologies in the construction of various facilities.

The structure of the material after reaching the desired hardness

That is why the question is so relevant, after what time does concrete gain strength and how does this affect the timing of construction?

Average rate of strength

Reinforcement cement-sand screed

Before answering the question, when concrete gains 70 strength, let's deal with what the number 70 means. In fact, this is a percentage designation of the brand parameters. Upon reaching this parameter, the structures and structures conditionally meet the requirements of GOST.

It is no secret that, in accordance with the assigned brand of concrete, not only the price is determined, but also the maximum load at the rate of kgf / cm ?, which can be exerted on concrete products without compromising the integrity of the product. That is why all industrial concrete goods are produced with a selling strength of 70% of the brand norm in the summer period and 90% in the winter period.

Since all industrially produced reinforced concrete products meet the requirements of GOST by default, construction companies can use it for their intended purpose immediately after receiving the ordered product.

Unlike construction organizations, which order concrete products from the factory, private users of the mortar must have a clear idea of ​​how long concrete gains strength when pouring formwork.

In the photo - work with concrete in the cold season

On average, technologists conduct branded inspection 28 days after the completion of the mortar pouring into the formwork. It can be assumed that this is the average time indicator necessary for a set of optimal hardness parameters.

In warm weather, during the first week after laying, intensive curing of the material takes place, up to the conditional 70% of the mark standard. During this process, the interaction of cement grains and liquid medium occurs until the formation of potassium hydrosilicates.

Important: The hardening process can continue even after a set of conditional 70% of the branded norm. For example, some concrete products with the initial grade of concrete M 200, after several years, acquire strength corresponding to materials with the mark M 400.

Time to remove the formwork

Formwork for the construction of the foundation

Now that we have decided on how many days concrete is gaining strength, we will determine when to proceed with the dismantling of the formwork.

  • If the concrete foundation is poured with your own hands, but taking into account the technological requirements and recommendations, you can proceed to dismantle the formwork in three days. During this time, optimum hardness parameters will be achieved, at which reinforced concrete can be cut with diamond circles. But despite this, the structure can be loaded not earlier than in a week.
  • If the pouring of structures and structures is carried out in winter time, the growth of strength is significantly slowed down.. Therefore, the formwork can be removed no earlier than a week. It is possible to load structures of this type and carry out diamond drilling of holes in concrete not earlier than in 2 weeks.

Important: Filling of the formwork in winter should be carried out with the use of special covering materials, since the uncovered solution will freeze and will not gain the required strength at all.

It should be understood that this instruction is important, since if you dismantle ahead of time, there is a high probability that cracks will appear in the thickness of the finished structure. But we must take into account the fact that it is also undesirable to overwork the formwork, since it prevents the free access of air, as a result of which the concrete dries unevenly.

Pace of setting and control methods of these parameters

In the photo - the foundation after the timely dismantling of formwork

Returning to how much concrete is gaining strength, consider the pace of gradual hardening:

  • For the first three days after laying under normal temperature conditions, the material gains about 30% of the brand strength.
  • After 7-14 days after installation under normal temperature conditions, the material gains more than 60% of the grade mark.
  • For 28 days after laying the concrete is able to gain 100% of the standard mark.
  • Within 90 days after laying, the material is able to gain up to 120% of the brand norm.
  • Further hardening and hardening of structures with the access of moisture also occurs, but the intensity of the process is an order of magnitude lower.

The hardest hardening of cement-containing solutions hinders the decrease in temperature. As a result of cooling, cement particles interact less actively with water. As a result, chemical reactions proceed extremely slowly.

Lowering the temperature to negative values ​​generally stops the hardening process. With a subsequent increase in ambient temperature, the material will harden, but in this case it is not necessary to count on the brand strength.

In the photo - the result of drying the solution in the process of setting.

At the same time, increasing the temperature in the thickness of the material allows to accelerate the rate of hardening. But, raising the temperature, it should be ensured that the solution in the formwork does not dry before the prescribed time.

For example, when concrete is heated with water vapor to a temperature of 80 ° C, it will take at least 16 hours to recruit 70% of grade strength. Thus, an industrial steaming is performed in the manufacture of piles and a number of other concrete products.

Important: Concrete should not be heated above 90 ° C, since at the temperature of boiling water a chemical reaction occurs, at which hardening of the cement-containing mortar becomes impossible.

Another point to which special attention should be paid is that the hardening of a cement-containing mortar is an exothermic process, during the course of which concrete produces heat. As a result, by increasing the temperature for more intensive curing, you risk over-drying the concrete, since the heat released during the exothermic process will be added to the heating temperature.

Conclusion

Now you know how much concrete is gaining strength and what factors determine the intensity of this process. As a result, you can make sure that the hardening of concrete structures is carried out within the framework of technological recommendations.

You can find more useful and informative information by watching the video in this article.

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